The present invention relates to a method and apparatus for grading, separating and breaking large clumps of agglomerated particulate material, and classifying the material according to size. This invention is particularly well suited for handling product from a direct reduction furnace in which particulates are subjected to high temperatures and often form clusters.
Devices of this type are known as roller screen conveyors or material classifiers. Such devices are shown in U.S. Pat. Nos. 2,966,267 and 4,405,050. However, none of the prior art devices have a positive breaking action which is developed by the present invention. U.S. Pat. No. 2,966,267 teaches a series of co-operating rolls aligned with parallel axes, each roll being provided with a plurality of equally spaced square cut grooves of uniform depth, the grooves being at an angle to the roll axis other than normal. U.S. Pat. No. 4,405,050 teaches a roller screen having a plurality of spaced rollers, without any grooving, but with the spacing so selected that only properly sized material will fall through the gaps between the rolls. It is clear that elongated material could readily fall through such spaces, resulting in unsatisfactory sizing of the processed material.
The apparatus comprises a series of screen rolls having radial projections, and a sizer roll having a series of offset discs that intermesh with the teeth of the screen rolls. The rolls reciprocate through a sufficient angle to move clusters onto the next roll or to break the clusters into smaller units which will fall through the recesses between the rolls and between the teeth. Preferably, the apparatus includes three or more rolls, each with similar projections. The sizer roll impacts clusters and oversize material, breaking it to acceptable size. The sizer roll shaft lifts out of its normal operative position to allow material remaining oversize to pass to a final screen roll, which directs the oversize material into a receptacle for further handling or crushing.